Akira Yamane, Satonari Akutsu, Thomas G.H. Diekwisch, and Ryoichi Matsuda. Satellite cells and utrophin are not directly correlated with the degree of skeletal muscle damages in mdx mice. Am J Physiol Cell Physiol. -To determine whether muscle satellite cells and utrophin are correlated with the degree of damage in mdx skeletal muscles, we measured the area of the degenerative region as an indicator of myofiber degeneration in the masseter, gastrocnemius, soleus, and diaphragm muscles of mdx mice. Further, we analyzed the expression levels for the paired box homeotic gene 7 (pax7), m-cadherin (the makers of muscle satellite cells), and utrophin mRNAs. We also investigated the immunolocalization of m-cadherin and utrophin proteins in the muscles of normal C57BL/10J (B10) and mdx mice. The expression level for pax7 mRNA and the percentage of m-cadherin-positive cells to the total number of cell nuclei in the muscle tissues in all four muscles studied were greater in the mdx than in the B10. However, there was no significant correlation between the muscle damage and expression level for pax7 mRNA (R=-0.140), nor was there a correlation between the muscle damage and the percentage of satellite cells to the total number of cell nuclei (R=- 0.411) in the mdx. The expression level for utrophin mRNA and intensity of immunostaining for utrophin in all four muscles studied were greater in the mdx than in the B10. However, neither was there a significant correlation between the muscle damage and the expression level for utrophin mRNA (R=0.231) in the mdx, although up-regulated utrophin was incorporated into the sarcolemma. These results suggest that satellite cells and utrophin are not directly correlated with the degree of skeletal muscle damages in mdx mice.